Bonded products and methods of fabrication therefor

ABSTRACT

This invention relates to a method of fabricating a bonded product comprising at least two components that are bonded together, the method comprising the steps of: a) bringing the components together; and b) heating the components; wherein at least one of the components comprises a nanomaterial and wherein steps (a) and (b) are performed in such a manner that the components are bonded together by heating at least part of the nanomaterial. The method allows the components to be welded together at lower temperatures than for prior art methods. The method also provides a more reliable form of bonding and improves the strength of the bond formed.

This invention relates to bonded products, to methods of fabricationtherefor and to bonding materials for use in such methods.

There are a number of ways in which bonded products, comprisingcomponents that have been bonded together, can be fabricated. Forexample the components may be bonded by welding, soldering, or by theuse of an adhesive. Welding involves melting the components so that theybond together. Alternatively one of the components may comprise abonding material such as an adhesive or a solder. For example if one ofthe components is a solder, then this component may be melted to form abond between the other components. Welding technology has a particularlyimportant role to play in the field of silicon microfabrication, whichis now an established manufacturing technique for producingmicromechanical devices. The technique provides for batch-processingminiaturised silicon devices of great diversity, for example micropumps,accelerometers, pressure sensors and microactuators. Manymicromechanical devices comprise several micromachined components, eachcomponent being formed from bulk crystalline silicon. Assembly of suchdevices often involves joining parts of silicon wafers, comprising bulkcrystalline silicon, together in a spatially precise, clean-roomcompatible manner. Silicon wafer bonding technology is therefore animportant aspect of device manufacture, for example to ensure thatassembled and packaged devices maintain operational reliability.

Many microfabricated devices incorporate electronic circuits, forexample circuits to perform in-situ signal processing or provide drivesignals for operating the devices. For many applications, the circuitshave to be protected from an environment in which the devices are to beused. Such protection is conventionally achieved by encapsulating thedevices in respective packages which are sealed by forming a packagehermetic seal under vacuum conditions.

There are presently two dominant conventional bonding processes forbonding silicon-based components together, namely “direct bonding” and“anodic bonding”. In direct bonding two or more components, comprisingbulk crystalline silicon, are assembled so that the surfaces to bebonded are in contact with each other. Heat is then applied to theassemble components so that the associated surfaces form a bond. Formany applications temperatures approaching 1000° C. are required beforethe bond can be formed. In contrast, anodic bonding is often employed toform bonds between silicon and silica components. It involves mating apolished surface of a silicon component to that of a silica component tobe joined together and then applying a high electric field across aninterface formed where the surfaces mate, thereby mutually polarisingthe surfaces to form an electrostatic bond at the interface. Duringanodic bonding, heating the components enhances bonding strengthachievable therebetween.

Both of these conventional bonding processes described above suffer adisadvantage that the components need to be heated in their entirety fordirect bonding and high electric field strengths are required for anodicbonding. In many situations, electronic circuits are not capable ofwithstanding annealing temperatures used in direct bonding and highelectric field strengths applied in anodic bonding; aluminiuminterconnections cannot withstand temperatures in excess of 450° C. forexample, whereas high electric fields can damage or ionise siliconnitride or silicon dioxide dielectric layers for example. Moreover,bonding strengths provided by direct bonding and anodic bonding areinsufficient in certain device applications where high reliability isparamount, for example for micromachined accelerometers which are to besubjected to peak acceleration forces in excess of 25000 g.

A demanding application for encapsulated microfabricated micromachineddevices is in biological environments where there are, for example,corrosive biological body fluids. Providing protection from such fluidsis particularly important for safety-critical applications where devicefailure cannot be tolerated, for example in amicrofabricated pace makerarranged to provide heart stimulation. A conventional approach forprotecting electronic circuits for use in biological systems is toencapsulate them within welded titanium boxes, titanium being abiocompatible material which biological systems accept by forming alayer of cells thereonto which thereby avoids biological rejectionproblems. This conventional approach was developed in the 1960's and1970's where, even in that era, hermetic seals were of a sufficientlyhigh quality to realise a remarkably low failure rate; J Buffet in anarticle in Medical Progress in Technology 1975 Vol. 3 page 133 reporteda failure rate of 13 out of 5800 implanted pacemakers encapsulatedwithin welded titanium enclosures over a three year period.

Although adoption of welded titanium enclosures has been acceptable tohealth care industries generally, the enclosures tend to be bulky whichexcludes their use in situations where miniaturisation is of primeimportance, for example for incorporation into an human inner ear regionto stimulate nerve endings therein. In a publication Advanced Materials7, 1995 pp. 1033, it is disclosed that silicon is potentially usable,instead of titanium, for enclosures for use in biological systems.Bonded silicon microfabricated micromachined components can thereby notonly form devices suitable for use in biological environments but alsoprovide their own encapsulation. However, especially in safety criticalapplications, seals provided between bonded silicon components must beextremely reliable. Conventional bonding techniques, for example directbonding and anodic bonding, are often insufficiently reliable for safetycritical applications. There is therefore a need for a more reliablebonding technique for bonding together semiconductor components.

Silicon welding has been previously investigated during the 1960's and1970's and is reported in an article by H Foll and D G Ast in theproceedings of the Ninth International Conference Electron Microscopy,1978, pp. 428-429. It was quickly abandoned as a reliable process forbonding silicon components because:

-   -   (a) welding of silicon components requires them to be heated to        an elevated temperature, namely bulk crystalline silicon has a        melting point temperature of 1414° C. which means that silicon        components to be bonded by conventional silicon welding have to        be heated to this temperature; such a high melting point is        incompatible with other microcircuit parts, for example        aluminium metallisation in an integrated circuit cannot        withstand temperatures in excess of 450° C.;    -   (b) silicon is a brittle material and exhibits a high thermal        budget for making it fuse during welding; this greatly increases        likelihood of fracture from thermally induced stresses.

It has been reported, by Goldstein in Appl. Phys. A62, p 33-7 (1996),that nanocrystals of silicon, comprising porous silicon, melt at lowertemperatures than bulk crystalline silicon. Melting temperatures as lowas 200° C., for 4 nm diameter nanocrystals of silicon have beenreported, which compares with melting temperatures of 1414 for bulkcrystalline silicon. Porous silicon may be fabricated by the chemicaldissolution of bulk crystalline silicon as described by L T Canham inAppl. Phys. Lett. Vol 57, p1046 (1990). Provided the pores aresufficiently closely spaced, nanocrystalline silicon can be formed bythis technique.

The following items of prior art are relevant to this invention: U.S.Pat. No. 5,628,848, WO 9606700, EP 0461 481 A2, GB 2337255, and GB2317885. U.S. Pat. No. 5,628,848 relates to the formation of multilayerstructures that are sintered together to form a strong bond between thelayers. The starting materials for the layers are in the form ofpowders. WO 9606700 relates to the fabrication of nanoscale particles.The invention also relates to the use of nanoscale particles to joincomponents together. EP 0461481 A2 relates to the use of nanocrystallinematerial in welding ceramic components together. GB 2337255 and GB2317885 relate to the use of silicon for biological and medicalapplication.

It is an objective of the invention to provide new bonded products andmethods for fabricating such products that reduce the above mentionedproblems. It is a further objective of the invention to provide newbonding materials for use in bonding methods.

According to a first aspect, the invention provides a method offabricating a bonded product comprising at least two components that arebonded together, the method comprising the steps of:

-   -   (a) bringing the components together; and    -   (b) heating the components;        wherein at least one of the components comprises a nanomaterial        and wherein steps (a) and (b) are performed in such a manner        that the components are bonded together by heating at least part        of the nanomaterial.

Step (b) may be performed prior to, during, or after step (a). Step (a)may comprise the step of abutting each component with the or at leastone of the components.

One of the components may comprise all of the nanomaterial.Alternatively each component may comprise nanomaterial.

The method may be used to weld or to solder the components together.

The method provides the benefit that the components can be weldedtogether at a lower bonding temperature compared to conventional bondingtechniques. This reduces the chances of fracture from thermally inducedstresses.

For the purposes of the invention, a nanomaterial is defined as amaterial comprising wires or particles having at least one dimension ina range of 1 nm to 20 nm. The nanomaterial may comprise ananocrystalline material; the nanocrystalline material comprisingcrystals having a smallest dimension in the range 1 nm to 20 nm.

Preferably the nanomaterial comprises wires or particles having asmallest dimension in a range in which fusion temperatures ofnanocrystals of the material are lower than corresponding bulkcrystalline material.

Advantageously at least one of the components comprises a semiconductingmaterial; more preferably at least one of the components comprisessilicon; yet more preferably at least one of the components comprisesbulk crystalline silicon.

Preferably at least one of the components comprises a semiconductingmaterial; more preferably at least one of the components comprisessilicon.

Advantageously the nanomaterial comprises a semiconducting material,more preferably the nanomaterial comprises silicon; yet more preferablythe silicon comprises porous silicon; even more preferably the poroussilicon has a porosity in the range 30% to 90%.

Preferably the method further comprises the step of forming at least oneof the components by: (i) taking a sample of silicon, and (ii) anodisingat least part of said silicon to form porous silicon.

In this way porous silicon may be formed on the surface of a componentto be bonded. The porous silicon is, at least initially, integral withthe silicon from which it is formed. The attachment of the poroussilicon to a component, or the rest of a component, assists inpositioning the nanomaterial for bonding.

Advantageously step (b) comprises the step of passing an electriccurrent through at least part of the nanomaterial; more preferably step(b) comprises the step of passing an electric current through at leastpart of the nanomaterial for a period between 20 and 80 seconds; yetmore preferably step (b) comprises the step of passing an electriccurrent through the nanomaterial and the or at least two of thecomponents.

The passage of an electric current allows heat to be applied at aparticular location. Heating occurs preferentially at the nanomaterial,due to its relatively high electric resistance, and not in thesurrounding region. The use of two electrodes may further restrictcurrent flow to the region between the electrodes. The use of asemiconducting material, as opposed to an insulator, opens the way forsuch electrical heating.

Porous silicon exhibits lower thermal conductivity than bulk crystallinesilicon. Bulk silicon has a thermal conductivity of 150 W m⁻¹ K⁻¹,whereas porous silicon exhibits thermal conductivities in a range of 140W m⁻¹ K⁻¹ to below 1 W m⁻¹ K⁻¹ depending upon porosity and associatednanocrystal diameter. Reduced thermal conductivity is beneficial becauseit allows higher localised temperatures to be achieved in porous siliconusing electrically resistive heating.

Porous silicon also exhibits a higher electrical resistivity relative tobulk crystalline silicon, localised heating for reliable bonding isachievable for lower electrical energy inputs compared to that requiredfor bulk silicon components devoid of porous silicon. This provides abenefit that the components do not need to be heated to as high atemperature as would be required for bulk silicon components devoid ofthe porous material and results in reduced thermal stresses to thebonded product.

Preferably step (b) comprises the step of melting the nanomaterial.

Preferably the method comprises the further step of locating the poroussilicon in an inert atmosphere prior to or during step (b). The inertatmosphere may comprise either nitrogen or a nobel gas; the nobel gasmay be selected from argon and helium.

Advantageously step (b) is performed at a pressure less than 1 mbar,more advantageously step (b) is performed at pressures less than 10⁻²mbar, yet more advantageously step (b) is performed at pressures lessthan 10⁻⁴ mbar.

Preferably the bonded product is a pharmaceutical product and the methodfurther comprises the step of forming and arranging the components insuch a manner that, once bonded, they are suitable for oral consumptionby a human or animal.

Advantageously the bonded product is a pharmaceutical product and themethod comprises the further step of forming and arranging thecomponents in such a manner that, once bonded, they are suitable foradministration to a human or animal in the form of a suppository.

Preferably the bonded product is an implant and the method comprises thefurther step of forming and arranging the components in such a mannerthat, once bonded, they are suitable for implantation into an animal orhuman body; more preferably the bonding is performed in such a mannerthat, when the components are implanted, a hermetic seal against animalor human body fluids is formed between the bonded components.

Advantageously the method comprises the further step of forming anintegrated circuit in one of the components, more advantageously theintegrated circuit is a silicon integrated circuit.

Preferably the method further comprises the step of removing any oxygenatoms bonded to the nanomaterial; more preferably the oxygen removingstep comprises the step of treating the nanomaterial with hydrofluoricacid.

Advantageously step (b) comprises the step of heating the nanomaterialby radiating the nanomaterial with laser radiation.

At least one of the components may be a micromachined component.

The method is of particular value in the fabrication of bonded productscomprising micromachined components. This is because micromachinedcomponents have a relatively low mass and are therefore particularlyvulnerable to thermal shock, and because the method may be performed atrelatively low temperatures.

According to a second aspect, the invention provides a bonded productcomprising fused nanomaterial characterised in that at least part of thefused nanomaterial forms a bond between a first part of the bondedproduct and a second part of the bonded product.

Preferably the bonded product comprises a semiconductor material, morepreferably the semiconductor comprises silicon; yet more preferably thesilicon comprises bulk crystalline silicon and/or polycrystallinesilicon and/or porous silicon.

Advantageously the fused nanomaterial comprises fused nanocrystallinesilicon, more advantageously the fused nanomaterial comprises fusedporous silicon.

Preferably the bonded product has a form and composition such that it issuitable for oral consumption by an animal or human body.

Advantageously the bonded product has a form and composition such thatit is suitable for inclusion in a suppository.

Preferably the bonded product has a form and composition such that it issuitable for implantation in an animal or human body; more preferably atleast part of the fused nanomaterial is arranged such that, whenimplanted, a hermetic seal against animal or human body fluids is formedbetween the first and second parts of the bonded product.

The bonded product may further comprise a micromachined component. Thebonded product may comprise an integrated circuit.

The method is of particular value in the fabrication of bonded productscomprising integrated circuits. This is because integrated circuits havedelicate circuitry that is particularly vulnerable to thermal shock, andbecause the method may be performed at relatively low temperatures.

According to a third aspect, the invention provides a bonding materialcomprising a nanomaterial.

Preferably the bonding material comprises a semiconducting nanomaterial;more preferably the semiconducting material comprises silicon; yet morepreferably the silicon comprises porous silicon; even more preferablythe porous silicon comprises comprises crushed porous silicon.

Advantageously the nanomaterial comprises a powder.

Preferably the bonding material further comprises a liquid component,the nanomaterial being distributed through the liquid component; yetmore preferably the bonding material is in the form of a paste.

In order that the invention might be more fully understood, embodimentsthereof will now be described, by way of example only, with reference toaccompanying drawings, in which:

FIG. 1 is an illustration of a bonded product according to theinvention;

FIGS. 2 a and 2 b are schematic diagrams of processing steps required tofabricate the product shown in FIG. 1;

FIGS. 3 a, b, and c are a schematic diagrams illustrating the formationof a bonded product comprising porous silicon;

FIG. 4 shows a sample of porous silicon, prior to heating to form aweld;

FIG. 5 shows micrographs of weld zones generated by welding according tothe invention; and

FIG. 6 shows a sample of fused nanocrystalline silicon located in theweld zone shown in FIG. 5.

FIG. 1 shows a first bonded product 110, according to the invention,comprising a first component 120 and a second component 130 that arebonded together by a fused nanomaterial 140. The bonded product 110 is acontainer and has a cavity 150 that is enclosed by the first and secondcomponents 120, 130. The first and second components 120, 130 of the areformed from bulk crystalline silicon; the fused nanomaterial 140 isformed from fused porous silicon.

FIG. 2 shows the processing steps involved in fabricating the firstbonded product 110 by a method according to the invention. FIG. 2 ashows the steps involved in fabricating the first and second components120, 130. FIG. 2 b shows how these two components 120, 130 are bondedtogether. A 1 □m thick silicon nitride layer 220 is deposited onto afirst silicon wafer to provide, when patterned, a stencil foranisotropic etching of cavities into the first wafer 210. The firstsilicon wafer comprises bulk crystalline silicon. An organicphotosensitive resist is deposited or spun onto the silicon nitridelayer 220, photolithographically exposed and developed. The first wafer210 and its associated layer 220 are then reactively ion etched toprovide etch windows such as 240 through the layer 220. The organicresist is then stripped off using oxygen plasma ashing or acetone.

The first wafer 210 is then immersed in a mixture of potassium hydroxidesolution and ethanol to isotropically etch a first set of recesses 250into the wafer 210. The potassium hydroxide etched wafer 210 is thenexposed to ion milling to remove remnants of the silicon nitride layer220. The first wafer 210 is then anodised in aqueous HF, as described inU.S. Pat. No. 5,348,618, to form a layer 260 of porous silicon. Theporous silicon comprises nanocrystalline silicon. The porosity of thelayer may be in the range 30% to 90%, and the thickness of the layer maybe in the range 100 nm to 10 μm. The processed first wafer 210 comprisesa multiplicity of first components 120 each having a first recess 250and a first porous silicon region 260. In other words the processedwafer 210 comprises a multiplicity of first components 120, eachcomponent being joined to its neighbouring component or components.

The same steps are applied to a second wafer 280 to yield a multiplicityof second components 130; each component 130 having a second recess 290and a second porous silicon region 300.

The porosification of the first and second wafers results inporosification of the whole surface that defines each cavity 250 andalso results in porsification of the surfaces that define the lips 270,300 located at the periphery of each cavity. The reason for both thelips 270, 300 and cavity defining surfaces being porosified in this wayis that these surfaces are all exposed to the electrochemical etchingprocess described in U.S. Pat. No. 5,348,618. For certain applicationsit may be desirable to prevent porosification in the cavities 250, inwhich case the cavity 250 surfaces would be protected by an HF resistantmask such as silicon carbide.

The processed wafers 210, 280 are dipped in hydrofluoric acid (HF) toremove any native oxide and are then promptly bought together so thattheir lips 270, 300 are mutually in contact to provide an assemblyindicated by 350. The assembly 350 is then placed in an evacuatedchamber at less than 1 mBar pressure and held between two spring-loadedpointed graphite electrodes 360 a, 360 b. A current of 2 Amperes is thenpassed through the assembly 350 from one of the electrodes 360 to theother; a potential difference of approximately 60 volts for a period of10 seconds is applied between the electrodes 360 a, 360 b to force this2 Ampere current through the assembly 350 to create a weld between theprocessed wafers 210 and 280. The island regions 270, 300 are fused bythe electric current, resulting in the formation of a first fused poroussilicon region 370. The assembly 350 is progressively stepped betweenthe electrodes 360 a, b to form a substantially continuous weld betweenthe wafers 210, 280.

The assembly 350 is then removed from the evacuated chamber, diamondscribed and diced to yield a multiplicity of first bonded products 110.The first and second components 120, 130 are bonded together, in themethod described above, when the processed wafers 210, 280 are weldedtogether; the fused porous silicon also being formed by the weldingprocess. The bonded product 110 is a sealed container.

Such sealed containers may be used for a number of biologicalapplications. Such applications partly stem from the fact that porousand polycrystalline silicon exhibit biocompatible and resorbableproperties, as disclosed in GB 9808052.6. A material is biocompatibleif, when implanted to a human or animal body, tissue forms a bond withthe material. A material is resorbable if, when implanted into an animalor human body, the material is corroded by the ambient body fluids andthe corrosion products are non toxic and readily excreted.

The bonded product 110 may be adapted to make it biocompatible byporosifying the external surfaces of the product 110 or by depositing alayer of polycrystalline silicon to the external surfaces, as describedin GB 9808052.6. A bonded product that has been adapted in this way may,for example, be implanted in a human body and bonded to human bone.

Alternatively the first bonded product 110 may be adapted for drugdelivery by porosifying at least part of the product to form a barrier.The porous barrier must extend from the cavity 150 to the exterior ofthe product 110. A product that has been adapted in this way may be usedfor drug delivery by introducing a drug into the container. The drug maybe introduced prior to the bonding process, for example by dissolvingthe drug in a suitable solvent and introducing the resulting solutioninto the first and/or second recesses 290, 250 by capillary action. Oncepresent in a human or animal body the body fluids corrode the porousbarrier, resulting in the release of the drug. For the purposes of thisspecification the term “body fluids” is taken to include blood, as wellas fluids present in the gastrointestinal, anorectal, and vaginalenvironments.

The first bonded product 110, which has been adapted for drug release inthis way, may be introduced into the human or animal body in a number ofways. The bonded product 110 may be administered orally, in which casethe container may be coated in an excipient coating to make the product110 more palatable to the human or animal. The bonded product 110 mayalso be introduced in the form of a suppository and may be surrounded bya suitable coating that facilitated insertion of the product 110 intothe animal or human. Finally the bonded product may be implanted, forexample by surgery, into the animal or human.

The first bonded product 110 may further comprise an integrated circuitformed in one of the components 120, 130 prior to the bonding process.Such an integrated circuit may be used in the control of drug release;for example controlling the rate of release.

There are a number of ways of fabricating a container, suitable for drugrelease, comprising a bonded product according to the invention. Asdescribed above the container may have a barrier comprising poroussilicon that separates the drug from the exterior of the container.Alternatively the barrier may comprise polycrystalline silicon.

The barrier to drug release may be formed before or after the bondingprocess. FIG. 3 illustrates a fabrication process by which the barriermay be fabricated before the bonding process. FIG. 3 a shows the stepsby which a third wafer fragment 410 may be processed, FIG. 3 b shows thesteps by which a fourth wafer fragment 510 may be processed, and FIG. 3c shows the step involved in bonding the third and fourth fragments 410and 510. The fragments 410 and 510 comprise bulk crystalline silicon.The fragments 410, 510 are anisotropically etched to yield thestructures 420, 520 respectively, and are then anodised to yield thethird and fourth components 430 and 530. The third component 430comprises a porous silicon barrier 440 and also comprises a third poroussilicon region 450. The fourth component 530 comprises a fourth poroussilicon region 540. The third and fourth components are bonded togetherby abutting the porous silicon regions 450 and 540 and passing anelectric current between the points c and d to yield a container 570having a fused porous silicon region 560 and a barrier 440.

Nanocrystalline silicon may be formed by anodising bulk crystallinesilicon to form porous silicon. The nanocrystalline silicon may bescraped from the surface of the bulk crystalline silicon to form apowder. The powder may be used as a bonding material for bonding bulkcrystalline silicon components together. The powder may be applied tothe interface between two components and a current passed through thepowder. Since the powder comprises nanocrystalline silicon it will meltat a lower temperature than the bulk silicon components to weld thecomponents together. The use of a powder is advantageous since it may beapplied to components in situations when it is not convenient to performanodisation; for example it may be applied when the component is noteasily anodised: The nanocrystalline silicon powder may be combined witha liquid or solid material to make the powder easier to handle. Forexample the liquid or solid material may assist in the application ofthe nanocrystalline silicon to the component to be welded; either byenhancing the cohesion of the nanocrystalline powder or by enhancing theadherence of the powder to the components that will be welded.

FIG. 4 shows a sample of porous silicon having a porosity of 50% andlayer thickness of 7 μm. The pores are too small to be seen at themagnification of the image (×7000). The sample shown in FIG. 4 was spotwelded in an Edwards E306 Vacuum Evapourator unit at 10⁻⁵ torr. The weldwas made by placing the sample in contact with a corresponding sample ofporous silicon; a current of 2 amps was then passed through the abuttedporous regions for a period of 10 seconds. The sample area for eachporous silicon sample was approximately 1 cm². FIG. 5 shows the twosamples after the current has been passed. The welded samples are brokenapart and FIG. 5 shows each sample in the region of the weld. FIG. 6shows part of one of the samples in the region of the weld; it shows asphere of fused nanocrystalline silicon. The sphere is formed as aresult of the porous silicon becoming molten, the surface tension of thesilicon causing the silicon to adopt the shape of a sphere. The sphereis sufficiently close, but not at the site of, the weld so that meltingof the silicon occurred without bonding.

A control experiment was also performed in which two bulk crystallinesilicon segments having polished front faces and an approximate surfacearea of 1 cm² were abutted and heated in the same manner as describedabove. A current of 2 amps was passed for a period of 60 seconds. Oncecurrent flow had ceased the samples were separated and the surfacesexamined by a XSEM at magnification of ×7000. No change in surfaceroughness was observed indicating that no weld had been formed.

Attempts to weld bulk silicon components devoid of abutting poroussilicon layers using the apparatus 500 have proved unsuccessful becausea sufficiently high interface temperature to cause fusion melting hasnot been possible to achieve.

Although welding of silicon components together at porous silicon layerinterfaces according to the invention is described above, components ofmaterials other than silicon, particularly semiconductor materials, canbe welded together in a similar manner, for example germanium andsilicon carbide. Moreover, porous layers which are welded togetheraccording to the invention need not be of similar chemical species totheir associated components, for example porous silicon layers may beformed onto germanium components which are subsequently welding togetheraccording to the invention.

1-28. (canceled)
 29. A method of fabricating a bonded product comprisingat least two components that are bonded together, the method comprisingthe steps of: (a) bringing the components together; and (b) heating thecomponents; wherein at least one of the components comprises ananomaterial, the nanomaterial comprising non-porous silicon, andwherein steps (a) and (b) are performed in such a manner that thecomponents are bonded together by melting at least part of thenanomaterial.
 30. A method according to claim 29 wherein at least one ofthe components comprises bulk crystalline silicon.
 31. A methodaccording to claim 29 wherein at least one of the components comprisessilica.
 32. A method according to claim 29 wherein the nanomaterialcomprises nanocrystals having diameters in the range 1 to 20 nm.
 33. Amethod according to claim 29 wherein the nanomaterial comprisespolycrystalline silicon.
 34. A method according to claim 29 wherein step(b) is carried out at an external pressure of less than 1 mbar.
 35. Amethod according to claim 29 wherein the method further comprises thestep of removing any oxygen atoms bonded to the non-porous silicon. 36.A method according to claim 35 wherein the oxygen removing stepcomprises the step of treating the non-porous silicon with hydrofluoricacid.
 37. A method according to claim 29 wherein the method comprisesthe further step of forming an integrated circuit in one of thecomponents.
 38. A method according to claim 29 wherein at least one ofthe components is a micromachined component.